Martini cadet Conversion to 7.62x39

[eljefeoz]

Gday All,
As above,am looking for info on converting a cadet to 7.62x39
idea is to use it primarily with CB, but J words? why not?
Barrel will be a .303 British, hopefully not too blown out , say a reasonable 0.312-0.314" if,such a beast is available.
As for the ejector and rimless- no worries there, conversion is not a problem.
Ideas from some one who has been there ,done that, AND:
what twist can I expect on the .303 and the range of CB which can be used.
NOT to forget, feasibility of using milsurp Czech or Bulgarian J word ammo?
TIA

[bruce drake]

You need to chat with JeffinNZ here on the forum and talk to him about his 303 Pygmy cartridge. think of a 7.62x39 with a 303 Rim. save a bit on the converting requirements with that Martini Cadet Rifle and have the same velocity and bullet selections as your original requested cartridge.

Bruce

[Rojelio]

Here's one I mocked up a while back to see if it's feasible. Used 303 British brass and Remington 125 SP (.310).
A friend gave me a new unfired barrel off of a mini mauser in 7.62x39 and I was thinking of matching it up with a greener cadet action I have.
Strictly a handloading proposition with the rim so cheap surplus ammo wouldn't work without a rimless extractor.
Still thinking about it.

[bruce drake]

http://castboolits.gunloads.com/show...ight=303+pygmy

Do a search on the forum 303 Pygmy. I found 5 pages of threads but here is the first one that Jeff posted.

Bruce

[eljefeoz]

Thank you Bruce& Rojelio-
Tony Small- Afro408 here- does a great job with a rimless ejector for the Martinis. And, he's done a similar .303 shortened to 40mm and modded to a 7.62x39.major pig killer!
It will be interesting to read up Jeff's mods. Let me give it a whirl
I am looking at the feasibility of a 'true' 7.62x39 on a Martini Cadet action, capable of handling J and CB.
Rojelio- Talk to Tony(Afro408) you may be able to get a rimless ejector going for your idea...
Cheers and Merry Christmas

[45 2.1]

I would be careful about this project. Many 310's were converted to 32 Special and other calibers when they were imported to enhance resale. The case head of the 7.62x39 is larger than that caliber. It also had some problems with pressure. Check your case head diameter versus the barrel shank thread root diameter. Full loads will eventually cause you some problems down the road.

[Outpost75]

In cartridges longer than the .357 Magnum, the case rim will hang up in the clearance groove on the top of the breech block, preventing positive ejection, and requiring partially extracted cases to be twisted and pried loose. I don't know what the SAAMI max. product average chamber pressure is for 7.62x39, but ComBloc steel cased military loads I tested in the 1980s ran about 50,000 cup in the government test barrel, using a pre-drilled case to compensate for the higher blanking pressure needed to puncture the steel case. I would expect pressures measured using current SAAMI practice would approximate that of .223 Remington ammunition, but you have a larger base diameter, so would have significantly greater backthrust. The Martini barrel shank diameter is also fairly small in diameter, so you would certainly want to run some thrust and yield calculations....

[Goatwhiskers]

I'm too lazy to look up actual case dimensions and barrel shank size, but I will say I've known of several conversions to .44Mag and they had problems with chamber swelling due to the remaining chamber wall thickness. I also knew one guy who converted his to .32Win Special and the light little gun kicked the snot out of him with factory ammo. Building a rifle that you might never shoot with anything but lighter loads is OK, but what if someone in the future decides to use hotter stuff? Food for thought. GW

[eljefeoz]

While I check out some more specs,esp the pressure/thrust/yield numbers, here's a rimless Martini extraction:

http://www.youtube.com/watch?v=Oaf5ugMw7KM

Cheers

[gnoahhh]

I'll chime in against such a conversion also. While the action "may" be strong enough, the problems alluded to regarding large-ish cases taking too much away from the strength of the small-ish barrel shank are very real IMO. If I wanted a .30 caliber cast bullet rifle with enough oomph to nail a deer at close range, I would look at making a .30 wildcat based on the .357 or shortened .357 Max case.

I too experienced the recoil of a .32WS built on a Cadet. It was unsettling, to say the least. All the small Martini's I have fooled with were in light .22 centerfire cartridges and gave sterling service.

The old saying that a Cadet action will hold any cartridge you can stuff into it is only partly true. Getting them in (and back out) is the stumbling block, combined with intruding too much into the small barrel shank.

[Afro408]

I'm not surprised that the 32 Win special conversion, using the existing .310 barrel, was and unsettling experience, especially if they were factory loads and .321" jacketed bullets, being fired down the .316" average size barrel. I'm not surprised that they also experienced excess pressure problems. I think that this combination is a bit too much for the cadet, but I have converted one to 32-40, because the barrel slugged at .320" and I would be shooting soft lead boolits at moderate velocities. It is very nice to shoot and I will be having no problems with it.
I also don't agree with 'Outpost75's comment about the larger rim preventing ejection. It's obvious that he hasn't tried it, because the cases in all the ones I have converted, no matter what calibre, eject cleanly out of the breech. It's all about how the conversion was done.

[Afro408]

Concerning the size of the barrel shank, on a Cadet, I would refer you to the dimensions of the Remington 760 pump rifle. Shank dia is .872, but the length of the thread is only .320!! I was horrified when I first worked on one of these. I thought that I was seeing things, but that's all that holds the barrel in to that locking extension.

[Afro408]

G'day fellas. At the request of the owner, I am posting on this build.
I was sent a Martini Cadet action, in good condition and barrelled in .222 rimmed and a new Ishapore made .303 Brit barrel.
The concept of this build was to have a light rifle, capable of easily killing large pigs and anything downsize from there.
It was decided to go with the 7.62x39 cartridge, because it would fit and component parts were readily available.
Shooting cast boolits from it would not be a problem.

I stripped the Cadet action and checked the internals for problems. This one had already had the firing pin bushed and the pin reduced in diameter. Essential steps necessary in any conversion to a higher pressure cartridge than the original .310 Greener.
I cut the thread from the .303 barrel and set it up in the lathe for machining. Sorry, but I forgot to take pics of this step.
The chamber was cut for the Ruskie cartridge and the Knox form reduced to .9" dia.
Barrel was cut down to 20" and re-crowned.
Here I am using a Dial Test Indicator, to get the bore running true, in my home made, very short chuck. Just one end of a spider, really.
I made this short chuck specifically for doing short barrels.


The other end of the spider, is the tail of the head stock spindle and I usually use the scribing block to get the barrel running true.


I gave the muzzle a flat crown, with 45* edges.


I modified the existing ejector, to one of my rimless ejectors.
https://www.youtube.com/watch?v=fZr1...Kw4Nqlyonvn5iQ

After the barrel was on and the ejector working properly, I test fired for proof, using Norinco millitary ball ammo. There were no problems.
The next job was to fit the supplied, 2.5-7x32 Weaver scope.
I machined up a piece of Pic rail and mounted it to the knox form and barrel. There is sufficient eye relief and loading clearance for the shell.
An old cut down Cadet forend was used till a new one can be made. The forend that was under the .222 barrel could not be adapted to this much slimmer barrel.


Yesterday I took it to the range and zeroed it with the Norinco ammo.
Bottom target was shot at 25yds and the top one at 100.

The extra little holes, in the bottom bull, are from my .22 Cadet and subsonic ammo.
There was a light breeze blowing from the right. I think it will shoot quite well, with good hand loads.

With a compact Red Dot, on the rail, this would be a great little carbine in the thick stuff.

[aussiebo]

Very nice ,very handy scrub gun.I spent a fair bit of time shooting in the New England area (sapphire city) but we never found any pigs

[Von Gruff]

Looks like a winner Afro and I have no doubt that eljefeoz will get it singing with cast, as he gets time off from his other duties.

[cwheel]

Can't speak to the safety of 3.62 X 39 in a Cadet. But Savage 24F has a simple extractor setup that might be perfect in this application. It uses a spring loaded plunger so the round can slip by and chamber. When the round is seated, the spring loaded plunger extends and allows the round to be extracted after firing. I have this setup in a Savage 24F that's chambered in .223 X 20ga. The spring loaded plunger extractor is used in the .223 barrel, works perfectly every time. The extractor used in the link above does the same thing except it is cammed sideways by the motion of the bolt. I think it might be much simpler to just move a small plunger on a spring. Food for thought. Pressure of the 7.62 X 39 round would be my concern. I understand several have re-barreled these successfully to 30-30 Winchester, a round that operates @ 40,000 psi. tops. 7.63 X 39 operates at 50,000 psi with factory rounds.
Chris